Seq. read performance is poor, seq. write is OK

The globalSAN iSCSI Initiator works reliably with an iSCSI target and sequential write performance is acceptable, but sequential read performance is very poor.

Resolution

Assuming your iSCSI target and network are configured properly, working properly, and sufficiently capable, you can expect to see around 100MB/s sequential write or read with the globalSAN iSCSI initiator over a GbE connection.

Performance tuning recommendations for all possible targets is not within the scope, but there is one performance issue that can be clearly identified and, depending on your target, may be easily and dramatically improved. If your target is providing normal sequential write throughput over GbE (e.g. ~100 MB/s) but considerably lower sequential read throughput (e.g. <30MB/s), then your issue may be improved by adjusting the net.inet.tcp.delayed_ack value for OS X.

In general, Dell and EqualLogic targets will provide much improved read performance with a value of '0' (whereas the default for OS X is '3').

To read your current setting in OS X, issue the following command:

sudo sysctl -a net.inet.tcp.delayed_ack

To change the value in OS X, issue the following command:

sudo sysctl -w net.inet.tcp.delayed_ack=3

To make the new value persistent across reboots you will need to define it in the /etc/sysctl.conf file.